1. Field of the Invention
The present invention concerns storage devices for magnetically recorded data and more particularly magnetic data storage devices employing a magnetic recording media made of a thin metallic film.
2. Description of the Prior Art
A wide variety of electronic instruments such as the increasingly common computer presently store data magnetically. Continuing improvements in the ability of these instruments to handle and manipulate increasing amounts of data in shorter time spans has correspondingly produced a need for storing data in ever increasing density on various types of magnetic data storage devices. As an example, it has become possible in recent years to store over eighty megabytes of data on one form of computer storage device (a 51/4 inch "Winchester" type hard disk) having the same data storage area as previous devices on which only five megabytes could be stored.
While available in a variety of forms, two of the more common types of magnetic data storage devices are those in which a magnetic data read/write head floats above the surface of a rapidly spinning rigid disk (Winchester type) and those in which the read/write head is in intimate contact with either a tape or a flexible disc (commonly called a floppy type disk). In either form, magnetic data is typically stored in a layer of magnetic recording media attached by various methods to some type of rigid or flexible substrate.
Typically a magnetic recording media layer is composed of either finely dispersed magnetically sensitive particles suspended in a polymeric binder or simply a continuous magnetically sensitive metallic thin film. Metallic thin films typically possess a greater density of magnetically sensitive material and, consequently, generally provide a greater data storage density.
Typically a metallic thin film magnetic recording media is applied to a substrate by either a "wet process" in which the metallic film is deposited on the substrate by a chemical plating process such as, for example, electroplating or electroless plating techniques or by a "dry process" such as vacuum evaporation, sputter coating, and ion plating techniques. In the case of dry processes, it is generally necessary to incline a target substrate at an extreme angle sometimes greater than eighty degrees to the direction of incidence of the metallic magnetic recording media vapor during the thin film deposition. Since the vapor impinges almost parallel to the substrate, the deposition rate becomes extremely slow with a resultant decrease in productivity and subsequent increase in cost.
In the case of wet processes, a certain number of imperfections are encountered in the uniformity of the metallic thin film coating and in the consistency of certain magnetic characteristics of the thin film coating such as remenance and coercivity. Data densities have now generally reached the point where the magnetic media surface area employed per unit of data stored is approaching the size of these defects. When a magnetic read/write head employed in such critical areas encounters one of these defects, errors occur in the data being stored on or read from the magnetic data storage device. Thus, there exists a need for improved magnetic data storage devices employing thin metallic films applied by a wet process with few or no coating inconsistencies or unintended variations in the magnetic characteristics of the thin film.
Previous efforts have been made to reduce the number of defects in a magnetic data storage device incorporating a metallic thin film. U.S. Pat. No. 4,254,189 to Fisher, for example, proposes the use of an intermediate plastic bonding layer between the substrate and a metallic thin film magnetic recording media to provide a smoother bonding surface for the thin film by filling in and masking topographical defects in the substrate. This approach, while providing a smoother surface, still allows for bonding defects between a metallic thin film and the smooth bonding layer. As another example, U.S. Pat. No. 4,430,387 to Nakagawa proposes the use of a 99.999% pure layer of aluminum having an anodized exterior surface to provide a better bonding surface for metallic thin films applied by sputter coating. An anodized surface layer, however, cannot be used in connection with metallic thin films applied by wet processes.
Thus there still exists a need for magnetic data storage devices incorporating metallic thin film magnetic recording media applied by wet chemical processes with few or no thin film coating defects.